The present invention relates to a control valve means for pressurized air-operated devices for driving fasteners into a workpiece.
A control valve means of this type is disclosed in EP-B 0 326 639. The device comprises an auxiliary valve spool having a second effective area communicating with a bore which is directed towards a trigger lever and which is connected to atmosphere when the trigger lever is in an inactive position. A portion of the trigger lever supports a sealing element sealingly closing the bore when the trigger lever is actuated. The sealing element is made of an elastomer and has a plug-like shape including a tappet tip at one end. It seats in the bore of an adjusting screw which in turn is provided in a threaded bore of the trigger lever.
When the trigger lever of this valve control means is actuated to move a first length of travel, a trigger valve which is defined by a plunger valve is released. This results in a single strike operation. When the release lever is further moved a second length of travel, the sealing element closes the bore and the device works in an automatic operation. There is the drawback that the release lever must be held in a position to maintain the automatic operation, in which position the conical tip of the seal element seals the opening. This requires a certain force resulting in a relatively clinched grip. This means vibrations are relatively intensively transmitted to the hand of the operator. There is a further drawback that the release lever has an offset portion adjacent the seal element such that the rearward grip portion only can be grasped with some comfort. The hand seizes the device adjacent the center of gravity which is located closer to the cylinder, thus the hand is ergonomically not particularly well positioned. There is a further drawback that repair and service of the valve control means are relatively expensive as a great number of components has to be disassemblied. In addition to the trigger lever, a valve plate including a throttle must be removed. Accordingly, a number of coaxially mounted components of the valve control means such as the main valve spool, the auxiliarly valve spool and the control sleeve as well as further parts adjacent the release lever become disassembled. As a rule, however, only those components which are dynamically strained in the automatic operation are required to be repaired or serviced. Again, reassembling the device including less stressed components is expensive.